Detailed Measurements of Characteristic Profiles of Magnetic Diffuse Scattering in ErB₂C₂

Abstract

Detailed neutron diffraction measurements on a single crystalline ErB2C2 were performed. We observed magnetic diffuse scattering which consists of three components just above the transition temperatures, which is also observed in characteristic antiferroquadrupolar ordering compounds HoB2C2 and TbB2C2. The result of this experiments indicates that the antiferroquadrupolar interaction is not dominantly important as a origin of the magnetic diffuse scattering.KEYWORDS: ErB2C2, TbB2C2, HoB2C2, antiferroquadrupolar ordering, diffuse scattering, long periodic magnetic structure, neutron diffraction IntroductionIn this paper, we report results of detailed neutron diffraction experiments for the rare earth compound ErB 2 C 2 , and discuss anomalous magnetic diffuse scattering which is also observed in the isostructural compounds, TbB 2 C 2 and HoB 2 C 2 , which exhibit characteristic antiferroquadrupolar (AFQ) orderings.The tetragonal compounds RB 2 C 2 (R=rare earth) with P 4/mbm symmetry 1-3 show various magnetic and quadrupolar behaviour due to coexistent competition between AFQ and antiferromagnetic (AFM) interactions. In particular, AFQ orderings in HoB 2 C 2 and TbB 2 C 2 are characteristic. HoB 2 C 2 exhibits an AFQ ordering at T Q =4.5 K under zero magnetic field, even though a magnetic ordered state exists between T Q and T N =5.9 K(> T Q ), 4-6 which means that the AFQ ordering is realised under the internal magnetic field caused by the magnetic ordering. The AFQ ordering in HoB 2 C 2 was also confirmed by resonant X-ray scattering experiments by Matsumura et al.7 On the other hand, TbB 2 C 2 exhibits an AFM ordering at T N =21.7 K, but shows no evidence of an AFQ ordering under zero magnetic field so far.

Magnetic phase transition in studied by neutron diffraction

“…The broad diffuse scattering like a ridge is also observed in HoB 2 C 2 . The satellite reflections and broad diffuse scatterings around ð1 0 0Þ are commonly observed in RB 2 C 2 (R ¼ Ce, Ho, Tb, Er), which is interpreted as reflecting the characteristic of the RKKY-type magnetic correlation of the RB 2 C 2 system [3,[8][9][10]. The satellite reflection of HoB 4 is also expected to be the characteristic of the RKKY-type magnetic interaction in the RB 4 system.…”

Magnetization process of tetragonal antiferromagnet,

“…The magnetic structure of the ground state is simply described by a propagation vector of [1 0 0] with the moments parallel to the c-axis. The intermediate phase between T t and T N shows an anomalous magnetic structure which consists of at least three components: (i) the broad satellites belonging to k ¼ ð1 þ d d 0Þ where d ¼ 0.11, (ii) the ridge-like component along the [1 0 0] and [0 1 0] directions between the neighboring satellites, and (iii) the broadest components with a nearly flat-top structure centered at the (1 0 0) reciprocal position [5][6][7]. This magnetic structure was also observed in the AFM phases neighboring to the AFQ phases of HoB 2 C 2 [8] and TbB 2 C 2 [9].…”